Super Typhoon Ragasa had sustained winds of 215 km/h with gusts of up to 295 km/h when it slammed into Panuitan island off Cagayan province on mid-afternoon Monday, Philippine forecasters said.
Tropical cyclones with sustained winds of 185 km/h or higher are categorised in the Philippines as a super typhoon, a designation adopted years ago to underscore the urgency tied to such extreme weather.
Ragasa was heading west and forecast to remain in the South China Sea at least into Wednesday, while passing south of Taiwan and Hong Kong before landfall on the Chinese mainland.
The Philippines' weather agency warned of coastal inundation, saying "there is a high risk of life-threatening storm surge with peak heights exceeding three meters within the next 24 hours over the low-lying or exposed coastal localities" of the northern provinces of Cagayan, Batanes, Ilocos Norte and Ilocos Sur.
Power was knocked out on Calayan Island and in the entire northern mountain province of Apayao, disaster-response officials said.
There were no immediate reports of casualties or further damage from Ragasa, which is locally called Nando.
Philippine President Ferdinand Marcos Jr suspended government work and all classes on Monday in the capital and 29 provinces in the main northern Luzon region.
More than 8200 people were evacuated to safety in Cagayan, while 1220 fled to emergency shelters in Apayao, which is prone to flash floods and landslides.
Domestic flights were suspended in northern provinces lashed by the typhoon, while fishing boats and inter-island ferries were prohibited from leaving ports due to rough seas.
Ragasa, the 14th major storm system to batter the Philippines this year, comes as authorities and both chambers of Congress investigate a corruption scandal involving alleged kickbacks that resulted in substandard or non-existent flood control projects.
Meanwhile, Taiwan's southern Taitung and Pingtung counties ordered closures in some coastal and mountainous areas, as well as on the outlying Orchid and Green islands.
Ragasa also forced the cancellation of afternoon flights to outlying islands and suspended various ferry services, the Central News Agency reported.
In Fujian province, on China's southeast coast, 50 ferry routes were suspended.
Officials in Shenzhen, the southern Chinese tech hub, planned to relocate about 400,000 people, including residents living in low-lying and flood-prone areas.
Shenzhen's airport said it will halt flights starting Tuesday night.
China's National Meteorological Centre forecast the typhoon would make landfall in the coastal area between Shenzhen city and Xuwen county in Guangdong province on Wednesday.
China's ruling Communist Party chief in Guangdong, Huang Kunming, urged departments across the region to minimise harm and "fully enter emergency state and war-ready state".
Ragasa is expected to sweep south of Hong Kong and Macao.
While Hong Kong's airport is expected to remain open, the city's airport authority said flights would be significantly reduced after Tuesday evening and most flight operations would be affected on Wednesday.
Hong Kong's flag carrier Cathay Pacific Airways said passenger flights scheduled to depart and arrive in the city after 6pm local time on Tuesday will be suspended, with more than 500 flight cancellations expected.
All schools in Hong Kong and Macao will be closed for the next two days.
Ragasa is expected to bring torrential rains and heavy winds to China's mainland coastal areas, starting Tuesday.
